1. Field of the Invention
The present invention relates generally to semiconductor processing, and more particularly to a method and apparatus for transferring a semiconductor die from an adhesive film hoop assembly to an output carrier pack.
2. Description of the Related Art
Semiconductor dies are typically manufactured by depositing on a wafer of material, such as silicon dioxide or gallium arsenide, a plurality of different layers of conductive, semiconductive and dielectric materials in precisely defined configurations. When the wafers are completed they are diced into individual dies, which are often very delicate. The individual semiconductor dies are difficult to handle during assembly of electronic apparatus because of their relatively small size and because certain types of semiconductor dies, such as laser diodes, are extremely fragile and thus easily damaged. A laser bar, also referred to as a bar of diodes, is formed by cleaving a section from a larger wafer on an adhesive film stretched over a hoop assembly. The wafer has a number of contiguous diodes, called the active strip, in a common substrate. The surface of the substrate in which the active strip is located is typically referred to as the p-side of the substrate. Typically, bonding pads, formed from a material such as gold, are formed on a surface of the semiconductor die to allow for connection of the semiconductor die to additional circuitry.
After the dies have been separated, they are placed on a die attach pad for bonding in an integrated circuit (IC) package or placed in a carrier for further packaging. This process is typically performed by a device known as a pick and place device. Each die is lifted by a collet and placed on a die attach pad or in a carrier. Die collets for placement of semiconductor dies are well known in the art.
FIG. 1 illustrates a typical commercially available pick and place device 10. Device 10 may include a microscope 12, an adjustable work platform 14, and a control arm 16. A collet 20 is secured at the end of the control arm which is designed to hold a semiconductor die (not shown) in position for die bonding or placement in a carrier or mounting member 18 positioned on the adjustable work platform 14.
FIG. 2 illustrates a conventional technique for transferring a semiconductor die from an adhesive film to a carrier which may be used by pick and place device 10 of FIG. 1.
A plurality of dies 40, usually rectangular in shape, are processed on a layer of adhesive film 32 by any technique as is known in the art. Adhesive film 32 is typically secured at its edges by clamps 34 as illustrated in FIG. 2. Disposed beneath adhesive film 32 is an expansion frame, such as for example a hoop frame 36, movable in the direction of arrow 38 such that expansion frame 36 pushes upward on film 32 distending it vertically and stretching it horizontally, providing a tense, flat surface on which the semiconductor dies 40 reside.
For placement of each die 40 on a die attach pad of an integrated circuit (IC) or in a carrier for further packaging, each die 40 is lifted from film 32 by collet 20 of pick and place device 10. Collet 20 has an aperture 46 at its distal end and a vacuum hole 48 extending through the length of collet 20 through which a vacuum pressure is exerted for lifting die 40. A die 40 is lifted by collet 20 by positioning aperture 46 over a die 20, exerting a vacuum pressure in the direction of arrow 52 and simultaneously moving an ejector pin 54 upwardly against the lower surface of film 32. Ejector pin 54 assists collet 20 in removing die 40 from adhesive film 32. Collet 20 is then moved upwardly away from film 32 by control arm 16 and positioned in another location for depositing the die 40 into another carrier (not shown), typically a pocket within a flat pack IC package.
There are problems, however, with the conventional pick and place operation as described with respect to FIG. 2. For example, the removal of die 40 from film 32 by collet 20 and placement into a carrier requires that the control arm 16 move very precisely and at high speeds to ensure that the die 40 are not damaged and the throughput maintained. Additionally, the manufacturing process of die 40 allows only for the p-side to be up, i.e., the p-side can only be formed on the surface 41 of die 40 facing toward the collet 20. It is preferable, for alignment purposes of the laser with external optics and also for thermal dissipation of the die 40, to mount the die 40 p-side down in the end circuit. Thus, the die 40, which is placed in an output carrier p-side up after being removed from film 32, must be re-oriented p-side down in another carrier before bonding in the end circuit. Currently this process is done using a mechanical flipping operation that is cumbersome and operator intensive, resulting in further risk of damaging the die 40 and increased production costs.
Thus, there exists a need for an apparatus and method for transferring a semiconductor die from an adhesive film to an output carrier that eliminates the control arm/vacuum collet assembly and associated handling steps and orients the die p-side down into the output carrier.